Method of assembling an electric motor



5, 1965 G. R. ANDERSON, JR 3,209,434

METHOD OF ASSEMBLING AN ELECTRIC MOTOR Original Filed Jan. 23, 1961 2Sheets-Sheet l I z 25 Z a /Z I 6 I /7 Z6 Z6 f w Z0 I 1 l 1 I INVENTOR.oeoawfifluoewswk W W ATTOF/VEYf Oct. 5, 1965 R. ANDERSON, JR 3,209,434

msmon OF ASSEMBLING AN ELECTRIC MOTOR Original Filed Jan. 23, 1961 2Sheets-Sheet 2 33 37 29 2e I I 432 5 2 27 IN VEN TOR.

WAMM

United States Patent 3 Claims. c1. 29 155.s

This invention relates to a method of assembling an electric motor.

The present application is a division made pursuant to requirement forrestriction in application 84,410 filed January 23, 1961 and entitledRotor Shaft Bearing and Method of Manufacture Thereof.

The invention is exemplified in the disclosed embodiment, which is animprovement upon U.S. Patent No. 2,904,709. The construction is one inwhich the rotor is rotatable upon a stationary shaft. The shaft issupported at one end only on a non-magnetic bracket spanning acylindrical bore in the stator field laminations. The bore is defined bycylindrically finished polar portions of the stator extending into closeproximity to the rotor at opposite sides of the bore. The rotor may ormay not be an armature of an electric motor.

It has always been very diflicult to locate the shaft directly upon andexactly aligned with the axis of the bore. In a motor, the rotor shouldbe at the center of the said cylindrical field pole surfaces. Theslightest offset or tilt of the shaft subjects the rotor to varyingmagnetic action which results in vibration and bearing wear and noise.In the past, the shaft has been pressed to a driven fit in a holeprovided in the bracket. Any mechanical error in the formation of thebracket, or its attachment to the stator laminations, or in the locationof the angle of the hole in the bracket, or in the drive fit of theshaft in such hole, has resulted in production of a motor which isobjectionable in the foregoing respects.

The present invention contemplates a procedure whereby the shaft isaccurately positioned by an expanding mandrel directly from the fieldpolar surfaces at opposite sides of the stator bore. The hole in thebracket is materially larger than the shaft in cross section. After theshaft is centered with precision on the axis of the cylindrical polarsurfaces it is connected with the bracket by casting or molding abonding insert to the shaft and to the bracket. The shaft is held in itsprecisely aligned and centered position until the cast material setsabout it. Three types of material have been found appropriate for use inthe casting operation. Any casting resin is usable, although lessdesirable at present because of the time required for set up. Type metalis also appropriate. However, the most satisfactory material found todate is conventional die casting zinc alloy.

Because the material which is cast about the end of the shaft to providea bond between the shaft and the bracket does not fuse with the bracket,the hole in the bracket is non-circular, being provided with keys orintegral splines or other irregularities to which the cast material mayadhere. The cast material may actually be of identical composition withthat of the bracket and still will not fuse thereto because the castmetal, in such a case, sets instantly upon contact with the previouslycast bracket. Its mass is so small that its heat cannot soften thesurface of the bracket. Moreover, any such cast material tends to shrinkslightly upon setup. In view of the irregular surface of the bracket thecast material will securely position the shaft notwithstanding theslight shrinkage and lack of fusion. In addition, this lack of fusionhas a very important and unexpected advantage in sound damping. Thejuncture between the bracket and the cast material in 3,209,434 PatentedOct. 5, 1965 which the shaft is embedded provides a barrier againstsound conduction.

Thus, not only does the structure and mode of manufacture as hereindisclosed assure concentricity and square ness and rigidity, withresulting quietness, but even such minimum vibration as may occur is nottransmitted to the stator frame of the motor. As a result, the motor issubstantially entirely noiseless in operation.

The uniformity of air gap also improves constant torque performance,starting characteristics, bearing life and efficiency of operation.

In the drawings:

FIG. 1 is a view showing in axial section a motor embodying theinvention.

FIG. 2 is a View in front elevation of the frame of a motor embodyingthe invention, the rotor being omitted.

FIG. 3 is a perspective view of the bracket which supports the armatureshaft.

FIG. 4 is a diagrammatic view in axial section through the stator, themandrel and the die shaft.

FIG. 5 is a fragmentary detail view taken in axial section on the line55 of FIG. 4.

The magnet frame 6 is made conventionally of stator laminations whichprovide the polar portions 7 and 8. For strength, the laminations may becontinuous about the stator bore but magnetic short circuiting isprecluded by reducing the cross section at 9 and 10.

The winding 15 is formed on a separate core 16 dovetailed at its endsinto the stator laminations of the frame 6.

The stator polar laminations are cylindrically finished at 17 to providea stator bore 18 to receive the rotor 20. This rotor is mounted on afixed shaft 25 supported from a bracket 26 which spans the stator bore.The bolts or rivets 28 extend through the laminations and the bracketand serve to maintain the frame in unitary assembly.

The prefabricated bracket 26 desirably comprises a die casting ofnon-magnetic metal such as zinc or type metal or an aluminum alloy. Thematerial preferably used is known as die casting zinc alloy Zamak No. 3,also identified as SAE No. 903; government specification QQZ363. Incomposition, it is primarily zinc with aluminum 3.5 to 4.3 percent andmagnesium 0.03 to 0.08 percent. Impurities should not materially exceed0.1 percent maximum. Those found in test of a typical alloy are copper0.007 percent; lead 0.005 percent; zinc 0.005 percent; and iron 0.100percent.

Centrally the bracket has a boss 27 through which extends a non-circularopening 12. The surface of the bracket about the opening 12 is rough orirregular to provide an anchorage for the shaft-positioning metal castin such opening as hereinafter described. In practice, the bridge memberis die cast to provide anchorage lugs or ribs or splines such as thoseshown at 29 in FIGS. 3 and 4.

For the reasons previously noted, the armature bearing post orstationary shaft 25 is positioned directly from the cylindical polarsurfaces 17 of the stator bore 18, whereby no other assembly toleranceWill in any manner affect its position. As one means of accomplishingthis result, the shaft is temporarily positioned in a self-centeringmandrel 30 which is inserted into the cylindrical stator bore to locatewith precision the axis of such bore on which the shaft 25 is to befixed. A set screw at 32 may be used to determine the axial position ofthe shaft 25 within the hole of mandrel 30. The end 33 of the shaft 25may project slightly beyond the outer surface of the boss portion 27 ofthe bridge. The mandrel 30 may be provided with an annular terminal ribat 34 which seats on the inner side of the boss 27 of the bridge as ameans of retaining in the opening 12 of the bridge the material to becast therein to anchor the shaft. Thus the mandrel is also a part of thedie assembly.

3 If the material is suitable for die casting, an external die 35 willdesirably be applied as shown in FIG. 4 to embrace the outer side of theboss 27 of the bridge and to provide a cavity at 36 enclosing the end.33 of the shaft 25. A very small duct 37 is provided to place theinterior of the die in communication with the conduit 38 from thepressure chamber in which the molten metal is stored for delivery to thedie.

With the assembly completed as shown in FIG. 4, the material to be castfor the retention of the shaft 25 is delivered through conduit 38 andduct 37 into the chamber 36 of die 35 to flow into the non-circularopening 12 about the end of shaft 25 and about the ribs orirregulariti'es 29 of the bracket 26. The duct 37 is so extremely smallthat the sprue breaks off when die 35 is removed, leaving no appreciablemark on the insert casting 40 which, as shown in FIG. 1 supports shaft25 from bracket 26 in the precise position in which such shaft waslocated by the expanding mandrel directly from the cylindrical surfaces17 of the stator. In other words, regardless of any irregularities inthe form or mounting of the bracket, the shaft will always be locatedwith precision in the exact center of the stator bore and in exactalignment with the axis of such bore.

As a result, the rotor will have precise concent'ricity and squarenesswith uniform air gap throughout. This will assure good starting torquein all rotor positions and constant torque performance in operation withsubstantially no vibration and excellent overall efficiency.

Not only is the rotor positioned with great precision but it is heldwith unusual rigidity on the desired axis of rotation. However, whetherthe imbedding material for the bearing post 25 is die cast or comprisesa casting resin, in either case there is no fusion between the castinsert 40 and the frame of the stator, the anchorage being mechanicaland the resulting joint providing a sound conduction barrier. Thepresent invention does not deal with prevention of imbalance in therotor but, even if imbalance is present and results in vibration, thevibration is largely confined to the shaft and transmission of vibrationto and through the stator frame is minimized by this construction.

I claim:

l. A method of mounting a non-rotatable shaft within the cylindricalstator opening between the poles of an electric motor having a statorwith such poles and having a rotor rotatable with respect to the shaft,such method including the steps of prefabricating a bracket with anaperture larger than said shaft and having a wall bounding said aperturewhich is provided with centrally converging surfaces for rigidconnection with the insert hereafter mentioned, the assembly oflaminations to comprise a stator frame having stator poles,cylindrically finishing the poles, assembling said bracket with thestator poles in a position spanning the opening, centering a shaft forthe rotor with precision by means of a jig supported directly from thestator poles, with a portion of the shaft projecting into the apertureof the bracket, casting between the shaft and the bracket an insert ofinitially fluid material, contrasting the material of the insert by thecooling of such material to wedge such material between the saidcentrally converging surfaces of the bracket and to shrink such materialupon the shaft for the rigid mounting thereof while maintaining theshaft rigidly positioned from the jig until such material has set, andthen removing the jig and leaving the shaft fixedly positioned from thebracket solely through such insert, the cast insert maintaining theshaft in precisely aligned position with respect to the cylindricallyfinished poles irrespective of tolerances in the bracket.

2. The method of claim 1 in which the prefabricating of the bracketcomprises a die casting operation including the casting of portions ofsaid bracket about the aperture as to provide circumferentially spacedlugs having the centrally converging surfaces aforesaid and definingsector-shaped spaces between said surfaces, thereby providing a key tomaintain the cast insert in rigid connection with the bracketnotwithstanding any shrinkage of the insert following the castingthereof within the bracket aperture.

3. The method of claim 2 including the step of positioning on thebracket a die having a cavity about the end of the shaft and providedwith an inlet for molded metal, the said casting of the insertcomprising a die casting operation involving the injection of metal intosaid cavity and'about the end 'of the shaft, andfollowed by the removalof the die from the bracket to expose the cast insert.

References Cited by the Examiner UNITED STATES PATENTS 598,540 2/98Soames 29-155.5 2,060,260 ll/36 Spengler 29155.5 2,781,165 2/57 Troller29155.5 2,814,744 11/57 Demetriou et al 31042 2,904,709 9/59 Lautner 3102,928,960 3/60 Macks 3l090 WHITMORE A. WILTZ, Primary Examiner.

JOHN F, CAMPBELL, Examiner.

1. A METHOD OF MOUNTING A NON-ROTATABLE SHAFT WITHIN THE CYLINDRICALSTATOR OPENING BETWEEN THE POLES OF AN ELECTRIC MOTOR HAVING A STATORWITH SUCH POLES AND HAVING A ROTOR ROTATABLE WITH RESPECT TO THE SHAFT,SUCH METHOD INCLUDING THE STEPS OF PREFABRICATING A BRACKET WITH ANAPERTURE LARGER THAN SAID SHAFT AND HAVING A WALL BOUNDING SAID APERTUREWHICH IS PROVIDED WITH CENTRALLY CONVERGING SURFACES FOR RIGIDCONNECTION WITH THE INSERT HEREAFTER MENTIONED, THE ASSEMBLY OFLAMINATIONS TO COMPRISE A STATOR FRAME HAVING STATOR POLES,CYLINDRICALLY FINISHING THE POLES, ASSEMBLING SAID BRACKET WITH THESTATOR POLES IN A POSITION SPANNING THE OPENING, CENTERING A SHAFT FORTHE ROTOR WITH PRECISION BY MEANS OF A JIG SUPPORTED DIRECTLY FROM THESTATOR POLES, WITH A PORTION OF THE SHAFT PROJECTING INTO THE APERTUREOF THE BRACKET, CASTING BETWEEN THE SHAFT AND THE BRACKET AN INSERT OFINITIALLY FLUID MATERIAL, CONTRASTING THE MATERIAL OF THE INSERT BY THECOOLING OF SUCH MATERIAL TO WEDGE SUCH MATERIAL BETWEEN THE SAIDCENTRALLY CONVERGING SURFACE OF THE BRACKET AND TO SHRINK SUCH MATERIALUPON THE SHAFT FOR THE RIGID MOUNTING THEREOF WHILE MAINTAINING THESHAFT RIGIDLY POSITIONED FROM THE JIG UNTIL SUCH MATERIAL HAS SET, ANDTHEN REMOVING THE JIG AND LEAVING THE SHAFT FIXEDLY POSITIONED FROM THEBRACKET SOLELY THROUGH SUCH INSERT, THE CAST INSERT MAINTAINING THESHAFT IN PRECISELY ALIGNED POSITION WITH RESPECT TO THE CYLINDRICALLYFINISHED POLES IRRESPECTIVE OF TOLERANCES IN THE BRACKET.